Use of powder-metallurgical pre-material for producing an NB alloy that is free of inclusions

ABSTRACT

One aspect is a method for producing an alloy, whereby the alloy consists of a first metal, a second metal, a third metal, and a fourth metal, and the first metal, the second metal, the third metal, and the fourth metal are selected from the group consisting of the metals, niobium, zirconium, tantalum tungsten. The method includes the steps of
         grinding the first metal to form a first metal powder and grinding the second metal to form a second metal powder;   mixing the first metal powder and the second metal powder to form a first blended powder;   generating a first blended body from the blended powder by a powder metallurgical route; and   generating the alloy by melting the first blended body and the remaining metals by a melt metallurgical route.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application claims priority to German PatentApplication No. DE 10 2009 056 504.3, filed on Dec. 2, 2009, which isincorporated herein by reference. This Patent Application is alsorelated to Utility Patent Application filed on Aug. 6, 2010, entitled“PRODUCING AN ALLOY WITH A POWDER METALLURGICAL PRE-MATERIAL” havingAttorney Docket No. W683.109.101/P11152 US

BACKGROUND

One aspect relates to a method for producing an alloy, whereby the alloyconsists of a first metal, a second metal, a third metal, and a fourthmetal, and the first metal, the second metal, the third metal, and thefourth metal are selected from the group consisting of the metals,niobium, zirconium, tantalum, and tungsten.

In medical technology, wires and tubes are needed for the production ofmedical components. Said wires and tubes are made, for example, ofalloys of multiple high-melting metals. In “Journal of the mechanicalbehavior of biomedical materials I,” (2008), p. 303-312, a method forproducing an alloy from the metals, niobium, zirconium, tantalum, andtungsten—which shall be referred to as NbTaWZr hereinafter forsimplicity reasons—is described. In the scope of said method, the fourmetals are each ground to form a powder and then melted. Despite theindividual metals being ground first, it has proven to be a disadvantageof said method that individual inclusions may arise in which only oneelement of the four metals specified above is present.

In production methods, which are also known, rods made of pure metalsare bundled and melted in a high vacuum, for example, by means of anelectron beam. It has proven to be disadvantageous in the case of alloysmade of tantalum, niobium, zirconium, and tungsten, that the elementwith the highest melting point is melted only incompletely. To someextent, larger lumps, for example, of tungsten, drop into the melt bathduring the melting process without mixing with the other components ofthe alloy. Referred to as inclusions or mono-elemental regions, suchnon-melted lumps of one of the alloy metals lead to failure of thematerial at a later time, when the alloy is drawn into a wire. This canlead to fissures or cavities arising at said inclusions. Moreover, saidinclusions render the processing more difficult. For example, theinclusions reduce the fatigue resistance and lead to corrosion of a wiremade of the alloy.

For these and other reasons there is a need for the present invention.

SUMMARY

One aspect is a method for producing an alloy, whereby the alloyconsists of a first metal, a second metal, a third metal, and a fourthmetal, and the first metal, the second metal, the third metal, and thefourth metal are selected from the group consisting of the metals,niobium, zirconium, tantalum, and tungsten. The includes grinding thefirst metal to form a first metal powder and grinding the second metalto form a second metal powder; mixing the first metal powder and thesecond metal powder to form a first blended powder; generating a firstblended body from the blended powder by means of a powder metallurgicalroute; generating the alloy by melting the first blended body and theremaining metals by means of a melt metallurgical route.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

Further advantages, features, and details of the invention are evidentfrom the subclaims and the description in the following, in whichseveral exemplary embodiments of the invention are described in detailmaking reference to the drawings. The features mentioned in the claimsand the description can be essential for the invention both as such andin any combination thereof. In the figures:

FIG. 1 illustrates a flow diagram of the method according to oneembodiment.

FIG. 2 illustrates a flow diagram of a first development of the methodaccording to one embodiment.

FIG. 3 illustrates another development of the method according to oneembodiment.

FIG. 4 illustrates a flow diagram of another embodiment of the methodaccording to one embodiment.

FIG. 5 illustrates a schematic view of a melt metallurgical processingwithin the scope of the method according to one embodiment.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

One embodiment provides a method for producing an alloy from the metals,niobium, zirconium, tantalum, and tungsten, in which the disadvantagesmentioned above are prevented, in particular to provide a method thatreduces the maximal size of the inclusions as compared to known methods.In addition, a use of the alloy produced according to the method isproposed. Also, an implantable medical device is proposed. Features anddetails that are described in the context of the method shall also applyin the context of the implantable medical device and use, and viceversa.

One embodiment discloses a method for producing an alloy, which ischaracterized in that

a) the first metal is ground to form a first metal powder and the secondmetal is ground to form a second metal powder;

b) the first metal powder and the second metal powder are mixed to forma first blended powder;

c) the blended powder is used to produce a first blended body by apowder metallurgical route;

d) the alloy is generated by melting the first blended body and theremaining metals by means of a melt metallurgical route.

One embodiment is based on combining two methods for producing an alloy.This allows the advantages of the powder metallurgical route and of themelt metallurgical route to be combined. Performing the tworoutes—powder metallurgical and melt metallurgical—to be illustrated inmore detail below sequentially results in alloys whose inclusions areless than 4 μm in size. In the context of one embodiment, the terms,inclusion or mono-elemental region, shall are used to refer to a regionin the alloy that comprises only one of the various metals of the alloy.This mono-elemental region consists of just one metal of the alloy andcontacts the other metals of the alloy only on its outside surfaces. Oneadvantage of the powder metallurgical route is that it allows for goodhomogenization and easy alloying to be achieved at low sinteringtemperatures. In one embodiment, these advantages are combined with theadvantages of the melt metallurgical route, that is, the high level ofpurity of the alloy that can be achieved and the feasibility of alloyinghigh-melting metals together.

In the context of one embodiment, the term, “powder metallurgicalroute,” denotes a manufacturing process, in which a metal object ismanufactured from a metal powder. The term, “powder metallurgicalroute,” includes the following manufacturing processes: hot pressing,sintering, hot isostatic pressing. Hot pressing involves shaping andcompacting a metal powder to form a metal object by exposure to a, forexample, uni-axial, pressure and temperature. Sintering involves a heattreatment, in which an object consisting of metal powder is compacted.In hot isostatic pressing (HIP), a metal powder that has been filledinto a mold is compacted to form a metal object with approximately 100%density (isostatic) by means of high pressure and high temperature.

Because of the high affinity for oxygen, it has proven to beadvantageous to melt refractory metals under vacuum conditions. Thisallows pre-existing impurities to be removed and gas inclusions inmetals to be prevented. In the context of one embodiment, the term,“melt metallurgical route,” is used to refer to a manufacturing process,in which a metal object is melted by exposure to an energy source in avacuum. The term, “melt metallurgical route,” includes, for example, thefollowing manufacturing processes: vacuum induction, electron beammelting, and arc melting. In vacuum induction, the metal object to bemelted is melted in a crucible by means of induction under vacuumconditions and then poured into a water-cooled crucible. In electronbeam melting, energy-rich electron beams are used under vacuumconditions to melt high-melting materials, which are then poured into aningot mold with a floor, which can be lowered, and cooled walls. In arcmelting, an arc is ignited between the metal object to be melted and anelectrode by means of high voltage and under vacuum conditions, whichcauses the material to melt.

The special feature according to one embodiment is that the methodutilizes a two-stage process. A powder metallurgical route is used firstfollowed by a melt metallurgical route. One embodiment provides for atleast the first and the second metal to each be ground and processed toform a blended powder. Said blended powder is then used by means of thepowder metallurgical route as the base for producing the first blendedbody. In order to meet one of the objects specified above, that is, toprevent the presence of mono-elemental inclusions in the finished alloy,it has proven to be advantageous if the mixing of the first metal powderand the second metal powder proceeds as part of a homogenization step.Said homogenization step can, if applicable, also be part of the powdermetallurgical route. This allows an even distribution of the secondmetal powder in the first metal powder to be attained. There are nopowder regions formed, in which just one metal is present. Rather, whatis attained by means of the homogenization step is that the mixing ratioof the two metal powders with respect to each other is maintained by theblended powder and/or the blended body. In this context, the term,“maintained,” is understood to mean that the same distribution of thefirst metal powder with respect to the second metal powder exists ineach spatial element within the blended powder and/or blended body aslong as the volume of the region concerned is at least 125-fold largerthan the volume taken up by a single grain of the first and/or secondmetal powder.

Any of the following methods, for example, can be applied in the scopeof the homogenization step:

-   -   Use of pre-alloyed powder    -   Coating of powder or    -   Mechanical alloying

The use of pre-alloyed powder proceeds as follows: a NbTaWZr bodyproduced by means of HIP is treated with hydrogen, which causes the bodyto become brittle. The body is then processed to form a powder bygrinding. Subsequently, the powder is aged in a vacuum at atemperature >600° in order to remove the H from the metal. Then thepowder can be compacted and sintered by the PM route. The followingprocedural steps result in the scope of homogenization by coating thepowder: the main alloy component (for example, Nb powder particles) canbe coated with a slurry (consisting of fine W powder and a bindingagent). Subsequently, the coated powder particles are compacted andsintered jointly by the PM route. The steps involved in the scope ofmechanical alloying are as follows: intensive mechanical treatment ofthe powder (grinding at high rotational speed with many grindingspheres) leads to local welding of individual powder particles to eachother. The high temperature produced in the procedure leads to diffusionbetween the welded particles which increases the adhesion significantly.The powder thus obtained is then compacted and sintered according to PMmethods.

One variant of a development of the method according to one embodimentis characterized in that at least three of the four metals are ground toform metal powders and mixed to form the first blended powder in stepsa) and b). Said blended powder is processed to form a first blended bodyby means of the powder metallurgical route. In this context, the weightfractions of the three metal powders correspond to the alloying ratiodesired later on. This variant of a development of the method accordingto one embodiment is characterized by its simplicity, since all itrequires is grinding three metal powders. In step d), the alloy isproduced by melting the first blended body made up of three metalpowders and the remaining metal by means of the melt metallurgicalroute. As before, a homogenization step can be integrated in order toensure that the first blended powder and/or the first blended body havean even distribution of the three metals.

A variant of a development that goes even further provides four metalsto be mixed in the steps a) and b), whereby the alloy is produced instep d) by melting the first blended body by means of a meltmetallurgical route. In said development of the method according to oneembodiment, the method includes the steps of

-   -   grinding the first metal to form a first metal powder, grinding        the second metal to form a second metal powder, grinding the        third metal to form a third metal powder, and grinding the        fourth metal to form a fourth metal powder,    -   mixing the first metal powder, the second metal powder, the        third metal powder, and the fourth metal powder to form the        first blended powder,

whereby the alloy is produced in step d) by melting the first blendedbody by means of the powder metallurgical route. Said variant of adevelopment of the method according to one embodiment is characterizedin that all four metals are converted to powder form such as is alreadyknown in the prior art. However, unlike the prior art, a powdermetallurgical route is used in order to ensure homogenization of thefour metals in the first blended powder. Only by this meansmono-elemental inclusions, in which only one of the four requisitemetals is present, can be prevented from arising in the finished alloy.As discussed, such mono-elemental regions quickly lead to corrosionand/or, if exposed to load for long periods of time, fatigue fracture ofthe alloy material.

Another development of the method according to one embodiment ischaracterized by

-   -   i. grinding the third metal to form the third metal powder;    -   ii. generating a first additional body from the third metal        powder by means of the powder metallurgical route;

prior to step d), and by the alloy being generated in step d) byconcurrent melting of the first blended body, the first additional body,and the remaining metal by a melt metallurgical route. This variant ofthe method is characterized in that a first additional body is generatedfrom the third metal, which first additional body is then melted inaddition to the blended body in the scope of the melt metallurgicalroute. The remaining—that is, fourth—metal can be integrated into themelt metallurgical route as raw material in the form of a rod or a bar.

Another variant of the method is characterized by

-   -   I. grinding the fourth metal to form a fourth metal powder;    -   II. generating a second additional body from the fourth metal        powder by means of the powder metallurgical route;

prior to step d), and by the alloy being generated in step d) byconcurrent melting of the first blended body, the second additionalbody, and the remaining metal by a melt metallurgical route. Thisvariant of the method is characterized in that a second additional bodyis generated from the fourth metal, which second additional body is thenmelted in addition to the blended body in the scope of the meltmetallurgical route. The remaining—that is, third—metal can beintegrated into the melt metallurgical route as raw material in the formof a rod or a bar. Moreover, the remaining metal can therefore beincorporated into the alloy as a first additional body in this case. Inthis context, three bodies generated by means of the powdermetallurgical route—the first blended body, the first additional body,and the second additional body—would be subjected to a meltmetallurgical treatment in order to generate the alloy. The use of threebodies that have been produced by means of the powder metallurgicalroute and contain the four claimed metals is advantageous in oneembodiment, in that the grain size of the individual metals is reducedfrom the onset by the grinding alone. Accordingly, this results in avery even and homogeneous alloy.

Another variant of a development of the method according to the oneembodiment is characterized by:

-   -   grinding the third metal to form a third metal powder and        grinding the fourth metal to form a fourth metal powder;    -   mixing the third metal powder and the fourth metal powder to        form a second blended powder;    -   generating a second blended body from the second blended powder        by means of the powder metallurgical route;

after step c);

-   -   and generating the alloy in step d) by melting the first blended        body and the second blended body by means of a melt        metallurgical route.

Said embodiment of the method according to one embodiment includes theformation of two blended bodies. Both the first blended body and thesecond blended body are generated from a blended powder each by means ofthe powder metallurgical route. In this context, each blended powdercontains two metals. Accordingly, the first and second blended bodiesare generated concurrently by means of the powder metallurgical route.As discussed, a homogenization can be carried out in the scope of thepowder metallurgical route. Said homogenization step ensures that thetwo metal powders contained in one blended powder each are distributedevenly and homogeneously.

Two metals whose melting temperatures are as similar as possible areground to form a blended body. This ensures that the melting of thefirst and/or second blended body in the melt metallurgical route iseven. In step d), the NbTaWZr alloy is then attained by melting thefirst blended body and the remaining metals, in the form of the secondblended body, by means of the melt metallurgical route. This variant ofthe method surprisingly facilitates the production of particularlyhomogeneous alloys. Accordingly, tests have illustrated that the desireddistribution of the alloy is present in a volume that is smaller than125-fold the largest powder diameter. Accordingly, even the finestscales illustrate no deviation from the desired composition for theNbTaWZr alloy to be attained.

The first and second blended body are then melted jointly by means ofthe melt metallurgical route in the subsequent step d). This canproceed, for example, by bombardment with electrons in electron beammelting. In the process, the melted particles of the blended bodies flowinto a water-cooled ingot mold and solidify therein as an alloy. In thisvariant of a development of the melt metallurgical route, the blendedbodies are arranged next to each other such that both are hit by theelectron beam and are thus melted concurrently. Said concurrent use ofthe melt metallurgical route ensures that melted particles of all fourmetals flow into the ingot mold and solidify therein as a homogeneousalloy whose inclusions are less than 10 μm in size. Said alloys can thenbe used, for example, for implantable medical devices. In the scope ofthe variant of the method according to one embodiment described here,the first blended powder can just as well be compacted by hot isostaticpressing (HIP). Subsequently, the HIP body is cut into oblong bars whichare melted jointly with the second blended body and combined to form analloy by means of the melt metallurgical route.

A variant of a development of the method according to one embodiment ischaracterized by the alloy comprising the following fractions of themetals:

-   -   0.5 wt-% to 10 wt-% zirconium,    -   0.5 wt-% to 9 wt-% tungsten,    -   20 wt-% to 40 wt-% tantalum, and    -   the remainder being the niobium fraction;

by the alloy, for example, comprising the following fractions of themetals:

-   -   0.5 wt-% to 2.3 wt-% zirconium,    -   2.5 wt-% to 4.5 wt-% tungsten,    -   24 wt-% to 32 wt-% tantalum, and    -   the remainder being the niobium fraction,

for example, by the alloy comprising the following fractions of themetals:

-   -   1.3 wt-% zirconium,    -   3.5 wt-% tungsten,    -   28 wt-% tantalum, and    -   the remainder being the niobium fraction.

According to one embodiment, the alloy consists of the four metals,niobium, zirconium, tantalum, and tungsten. It is self-evident that thisalloy also includes the inevitable impurities. Although the alloy is toconsist of the four specified metals in the end, inevitable impuritiesof the four metals cannot be prevented in the scope of the productionprocess. Said inevitable impurities should obviously also become part ofthe alloy with the aim being to keep them as low as possible. It hastherefore proven to be preferred in one embodiment to use the fourmetals at the following purities:

-   -   zirconium more pure than 99.9%, in particular more pure than        99.95%, particularly preferred more pure than 99.995%,    -   tungsten more pure than 99.9%, in particular more pure than        99.95%, particularly preferred more pure than 99.995%,    -   tantalum more pure than 99.9%, in particular more pure than        99.95%, particularly preferred more pure than 99.995%,    -   niobium more pure than 99.9%, in particular more pure than        99.95%, particularly preferred more pure than 99.995%.

Reduction of the impurities to the levels specified above allows alloysto be produced that are biocompatible. Said biocompatible alloys arewell-suited for use for implantable medical devices.

Another development is characterized by the first metal being tantalum,the second metal being tungsten, the third metal being niobium, and thefourth metal being zirconium. In the context of the method for producingtwo blended bodies from two blended powders as described above, it hasproven to be advantageous in one embodiment to produce the first blendedpowder from the metals, tantalum and tungsten. Accordingly, the secondblended powder is made up by niobium and zirconium. Tantalum andtungsten have similar melting points and can be homogenized.Accordingly, this results in a particularly even alloy which comprisesno mono-elemental inclusions.

In order to attain particular purity of the alloy and to further reducethe size of any inclusions, it has proven to be advantageous in oneembodiment to supplement the method to the effect that the method, afterstep d), comprises the step of

-   -   e) melting the alloy by means of the melt metallurgical route.

In the scope of procedural step e), the alloy generated in step d) ismelted again. After the alloy generated in step d) has solidified, itcan be melted again by means of the melt metallurgical route.Accordingly, it is conceivable, for example, to melt the alloy from stepe) in a vacuum using an electron beam. Any inclusions, which already areless than 4 μm in size, can be further reduced in size by the repeatedmelting. A further development of said variant of a development providesfor step e) to be carried out multiply. Accordingly, it has proven to beadvantageous in one embodiment to perform step e) two to ten times, andin one embodiment three to five times. Repeated melting of the alloy bymeans of the melt metallurgical route further reduces the size of theinclusions. Accordingly, it has been possible to realize inclusion sizesof clearly less than 1 μm, in one embodiment less than 0.2 μm, by meansof melting three to five times in the scope of step e). Alloys withinclusions of this size can be used to advantage in one embodiment, forimplantable medical objects. Inclusions of this size have a negligibleinfluence on the fatigue resistance of the finished product.

Another variant of a development of the method according to oneembodiment is characterized in that the first metal is ground to formthe a first metal powder with a first powder particle size of between 4μm and 0.1 μm and/or the second metal is ground to form the second metalpowder with a second powder particle size of between 4 μm and 0.1 μm, inone embodiment between 4 μm and 1 μm. In the scope of the method, boththe first and the second metal each are ground to form metal powder.Depending on the development of the embodiment, the third metal also canbe ground to form a third metal powder and/or the fourth metal can beground to form a fourth metal powder. In order to ensure that theinclusions, that is, those regions in the alloy, in which only a singlemetal is present in elemental form, are small in size, the metals mustbe ground fine enough during the preparation phase for the powderparticle size of the individual metal powders to be between 4 μm and 0.1μm, in one embodiment between 4 μm and 1 μm, since the size of thepowder particles is correlated to the size of the inclusions. In thecontext of one embodiment, the term, “powder particle size,” is used torefer to the maximal size of those particles of the metal powder that isattained in the scope of grinding and ensuing screening. Accordingly,the size of the mesh of the sieve used to screen the metal powder aftergrinding indicates the upper limit of the powder particle size.According to one embodiment, the required powder particle size shallspecify the maximal size of a particle of the metal powder. No particleof the metal powder shall be of a size larger than the powder particlesize, but can be of any smaller size.

Due to the grinding of the first metal and second metal, and in oneembodiment, of the third metal and/or fourth metal also, the size of theinclusions of the first and/or second and/or third metal and/or fourthmetal in the alloy is between 10 μm and 10 nm. If, in addition, step e)according to one embodiment is performed multiply, it is feasibleaccording to one embodiment for the size of the inclusions to be between4 μm and 20 nm, and in one embodiment between 2 μm and 50 nm. Said sizeis non-objectionable for the use in alloys of implantable medicaldevices.

A use in an implantable medical device of an alloy that was manufacturedaccording to any one of the methods described above is also claimed. Themethod according to one embodiment enables the production of an alloythat is particularly well-suited for implantable medical devices, in oneembodiment, since no non-melted lumps of an alloy metal—also calledmono-elemental region—arise. Rather, all alloy metals are melted suchthat no mono-elemental regions arise that might lead to fissures orcavities in implantable medical devices that are made up of an alloythat is produced according to one embodiment. An implantable medicaldevice that is characterized by the implantable medical device being, atleast in part, made up by an alloy is also claimed, whereby the alloy isproduced according to any one of the methods described above. It hasproven to be a preferred variant of a development of said implantablemedical device according to one embodiment, that the implantable medicaldevice is a stent or a precursor product of a stent or an electrode or acardiac pacemaker casing or a cable or an electrical lead. All medicaldevices mentioned above have diameters or wall thicknesses that are onthe same order of magnitude as the size of non-melted lumps of an alloymetal in known production procedures. Accordingly, fissures or cavitiesarise in medical devices according to the prior art if they are producedfrom said alloys according to known methods. The same is not true if themedical device is made up of an alloy that is produced according to themethods according to one embodiment.

An issue, on which the method according to one embodiment for producingan alloy is based, is that not all metals are distributed evenly in thefinished alloy, for example, in the case of high-melting refractorymetals, but rather regions—also called inclusions or mono-elementalregions—are formed, in each of which only one metal of the variousmetals used for the alloy is present in pure form. Inclusions of thistype can significantly reduce the fatigue resistance of the finishedproduct. In order to overcome this disadvantage, one embodimentdiscloses a method for producing an alloy from the refractory metals,niobium, zirconium, tantalum, and tungsten, whereby the alloy 100comprises a first metal 10, a second metal 20, a third metal 30, and afourth metal 40. In this context, a fusion of said metals 10, 20, 30, 40to form a combination metal is referred to as alloy 100. The specialfeature according to one embodiment is that first a powder metallurgicalroute and subsequently a melt metallurgical route is used sequentially,that is, one after the other, for producing the alloy.

FIG. 1 illustrates a flow diagram illustrating the method according toone embodiment for producing the alloy 100. The first metal 10 and thesecond metal 20 are used as the basis in this context. Firstly, thefirst metal 10 is ground to form a first metal powder 11. Concurrentlyor subsequently, the second metal 20 can be ground to form a secondmetal powder 21. In this context, it has proven to be advantageous forthe first metal 10 to be ground to form a first metal powder 11 with aparticle size between 10 μm and 0.1 μm. The same applies to the secondmetal that is ground to form a second metal powder 21. Subsequently, thefirst metal powder 11 and the second metal powder 21 are mixed to form afirst blended powder 43. Said first blended powder 43 comprises thefirst metal powder 11 and the second metal powder 21 with theirdistribution corresponding to the one which the two metals 10, 20 are topossess later in the alloy 100. The blended powder 43 is used togenerate a first blended body 45 by means of the powder metallurgicalroute 50. The powder metallurgical route 50 can, for example, be aprocess of hot isostatic pressing (HIP). In the process, the firstblended powder 43 is compacted to form the blended body 45 by theinfluence of pressure and heat. Subsequently, the first blended body 45can be cut into oblong bars, which are then melted by means of the meltmetallurgical route 60 in order to form the alloy 100. The meltmetallurgical route also includes melting of the remaining metals, 30,40. Accordingly, the alloy 100 is generated by melting the first blendedbody 45 and the remaining metals 30, 40 by means of the meltmetallurgical route. The bodies of the remaining metals can be a bar ora rod that comprises the respective metal in pure form. Said bodies ofthe third and fourth metals 30, 40 are bundled with the first blendedbody 45 at a ratio which corresponds to the later ratio of the metals10, 20, 30, 40 in the alloy 100.

In the context of one embodiment, the term, powder metallurgical route,shall in particular refer to the manufacturing of a product using thefollowing steps, whereby each step can take a different form:

1) generating a metal powder 11, 21,

2) shaping, and

3) heat treatment.

For manufacturing an alloy 100 by means of the powder metallurgicalroute 50, metal powders of the metals having powder particle sizesbetween 10 μm and 0.1 μm are needed. The type of powder production has amajor impact on the properties of the powders. Mechanical methods,chemical reduction methods or electrolytic methods as well as thecarbonyl methods, spinning, atomizing, and other methods can be used forproducing the powder. The shaping involves compaction of the metalpowder in pressing tools under high pressure (between 1 and 10 t/cm²(tons per square centimeter) to form green compacts. Other feasiblemethods include compaction by vibration, slip casting method, castingmethods and methods involving the addition of binding agents. In heattreatment (also called sintering), the powder particles are solidlybonded at their contact surfaces by diffusion of the metal atoms. Thesintering temperature of single-phase powders is between 65 and 80% ofthe solidus temperature.

FIG. 2 illustrates another development of the method according to oneembodiment. In a first step, the three metals 10, 20, 30 each areseparately ground to form a first metal powder 11, second metal powder21, and third metal powder 31. Subsequently, the first metal powder 11,second metal powder 21, and third metal powder 31 are mixed to form thefirst blended powder 43. Then the blended body 45 is manufactured fromthe blended powder 43 by means of a powder metallurgical productionprocess 50. A homogenization step can also be carried out in the scopeof the powder metallurgical route 50 and is utilized to ensure that thedistribution of the individual metal powders in the blended powder 43 isas even as possible. Subsequently, the first blended body 45 and theremaining metal 40—that is, the fourth metal—are melted by means of themelt metallurgical route 60. This results in the desired alloy 100. Saidalloy 100 can be subjected to the melt metallurgical route 60 again inorder to attain further reduction of the size of any mono-elementalregions that may still be present. Said mono-elemental regions can thenbe of a size of less than 0.5 μm, one embodiment less than 0.1 μm.

FIG. 3 illustrates a variant of a development of the method according toone embodiment. Said variant of a development is characterized by

-   -   grinding the first metal 10 to form a first metal powder 11,        grinding the second metal 20 to form a second metal powder 21,        grinding the third metal 30 to form a third metal powder 31, and        grinding the fourth metal 40 to form a fourth metal powder 41;    -   mixing the first metal powder 11, second metal powder 21, third        metal powder 31, and fourth metal powder 41 to form the first        blended powder 43;

whereby, the alloy 100 is generated in step d) by melting the firstblended body 45 by means of the melt metallurgical route 60.Accordingly, all four metals 10, 20, 30, 40 are processed to form afirst blended body 45 in this variant of a development. The scope ofgenerating the first blended body 45 by means of the powdermetallurgical route 50 includes a homogenization for production reasons,in contrast to the prior art. The homogenization can be intensified bythe homogenization step mentioned above. It is thus ensured that nomono-elemental regions arise in the finished alloy 100 which might leadto fissures and/or damage during the use of the alloy 100 as basematerial of an implantable medical device, which would impair theserviceability of the implantable medical device. As discussed above,the alloy 100 is generated by means of the melt metallurgical route 60after the first blended body 45 is generated.

Another development of the method according to one embodiment isillustrated in FIG. 4 and is characterized in that the first metal 10and the second metal 20 each are ground to form metal powders 11, 21 andsubsequently mixed to form a first metal powder 43. Said first metalpowder 43 is then used as the basis for generating the first blendedbody 45 by means of the powder metallurgical route. Subsequently orconcurrently, the third metal 30 and the fourth metal 40 are ground toform a third metal powder 31 and a fourth metal powder 41, respectively.Said two metal powders 31, 41 are also mixed to form a second blendedpowder 44. A homogenization can also proceed, as before. Subsequentlyand/or partly concurrent with the homogenization step, the powdermetallurgical route 50 is applied. A second blended body 46 is obtainedon the basis of the second blended powder 44. Said two blended bodies45, 46 each contain the powders of the individual metals 10, 20, 30, 40at the same ratio as desired to be present later in the alloy. The twometal powders are mixed such that the two highest-melting metals areintegrated into the first metal powder 43. Accordingly, it is expedientto combine tantalum and tungsten in the first blended powder 43.Accordingly, the second blended powder 44 contains niobium and zirconiumwhich have comparable melting temperatures. Accordingly, a starting basethat is even and can be converted into the later alloy is thus created.Subsequently, the alloy 100 is generated in step d) by means of the meltmetallurgical route 60 by melting the first blended body 45 and theremaining metals 30, 40 in the form of the second blended body 46. Ithas proven to be advantageous in one embodiment for alloy 100 tocomprise the following fractions of the metals 10, 20, 30, 40: 0.5 wt-%to 10 wt-% zirconium, 0.5 wt-% to 9 wt-% tungsten, 20 wt-% to 40 wt-%tantalum, and the remainder being accounted for by the niobium fraction,in particular for the alloy 100 to comprise the following fractions ofthe metals 10, 20, 30, 40: 1.3 wt-% zirconium, 3.5 wt-% tungsten, 28wt-% tantalum, and the remainder being accounted for by the niobiumfraction.

The purpose of FIG. 5 is to illustrate the melt metallurgical route 60by means of an electron beam melting process. As has been discussedabove, a second blended body 46 can be generated from the third metal 30and the fourth metal 40 by means of the powder metallurgical route 50.Said blended body 46 is then arranged spatially next to the firstblended body 45 in a vacuum chamber. An electron source 70 generates anelectron beam 71 that knocks single metal particles from the first andsecond blended bodies 45, 46. In this context, the first, second, third,and fourth metals 10, 20, 30, 40 should be ground to a powder particlesize between 10 μm and 0.1 μm for the inclusions of the first metal 10and/or the second metal 20 and/or the third metal 30 and/or the fourthmetal 40 in the alloy to be between 4 μm and 10 nm in size. The meltedmetal particles flow into the ingot mold 110 where they form the alloy100. For the alloy 100 to solidify quickly, the walls 117 of the ingotmold are cooled. A floor 115 that can be lowered ensures that the pathto be traveled by the melted metal particles until they impact thesurface of the alloy 100 is always the same.

A development of the method according to one embodiment provides thealloy 100 to be melted again after step d) by means of the meltmetallurgical route 60. Multiple melting of the alloy 100 by means ofthe melt metallurgical route 60 allows the size of the inclusions of thefirst metal 10 and/or the second metal 20 and/or the third metal 30and/or the fourth metal 40 in the alloy to be reduced further. It hasproven to be advantageous in one embodiment to melt the alloy 100 threeto five times by melt metallurgical means after generating it. In theprocess, it is feasible to attain inclusions of the first metal 10and/or the second metal 20 and/or the third metal 30 and/or the fourthmetal 40 that are between 4 μm and 20 nm in size. Inclusions of thistype have negligible impacts on the fatigue resistance of the alloy inimplantable medical devices.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A method for producing an alloy, whereby the alloy consists of afirst metal, a second metal, a third metal, and a fourth metal, and thefirst metal, the second metal, the third metal, and the fourth metal areselected from the group consisting of the metals niobium, zirconium,tantalum, and tungsten, characterized by the method comprising steps of:a) grinding the first metal to form a first metal powder and grindingthe second metal to form a second metal powder; b) mixing the firstmetal powder and the second metal powder to form a first blended powder;c) generating a first blended body from the blended powder by means of apowder metallurgical route; d) generating the alloy by melting the firstblended body and the remaining metals by means of a melt metallurgicalroute.
 2. The method according to claim 1, further comprisingadditionally grinding one of the third and fourth metals to form one ofa third or fourth metal powder and additionally mixing one of the thirdor fourth metal powder with the first and second metal powders to formthe first blended powder in steps a) and b).
 3. The method according toclaim 1, characterized by i. grinding the third metal to form the thirdmetal powder; ii. generating a first additional body from the thirdmetal powder by means of the powder metallurgical route before step d),and generating the alloy in step d) by concurrent melting of the firstblended body, the first additional body, and the fourth metal by meansof the melt metallurgical route.
 4. The method according to claim 1,characterized by I. grinding the fourth metal to form a fourth metalpowder; II. generating a second additional body from the fourth metalpowder by means of the powder metallurgical route before step d); andgenerating the alloy in step d) by concurrent melting of the firstblended body, the second additional body, and the third metal by meansof the melt metallurgical route.
 5. The method according to claim 1,characterized by grinding the third metal to form a third metal powderand grinding the fourth metal to form a fourth metal powder; mixing thethird metal powder and the fourth metal powder to form a second blendedpowder; generating a second blended body from the second blended powderby means of the powder metallurgical route after step c); and generatingthe alloy in step d) by concurrent melting of the first blended body andthe second blended body by means of the melt metallurgical route.
 6. Themethod according to claim 1, characterized by the alloy comprising thefollowing fractions of the metals: 0.5 wt-% to 10 wt-% zirconium, 0.5wt-% to 9 wt-% tungsten, 20 wt-% to 40 wt-% tantalum, and the remainderbeing accounted for by a niobium fraction.
 7. The method according toclaim 6, characterized by the alloy comprising the following fractionsof the metals: 1.3 wt-% zirconium, 3.5 wt-% tungsten, 28 wt-% tantalum,and the remainder being accounted for by the niobium fraction.
 8. Themethod according to claim 1, characterized by the first metal beingtantalum; the second metal being tungsten; the third metal beingniobium; and the fourth metal being zirconium.
 9. A method for producingan alloy comprising: grinding a first metal to form a first metal powderand grinding a second metal to form a second metal powder; mixing thefirst metal powder and the second metal powder to form a first blendedpowder; generating a first blended body from the blended powder by meansof a powder metallurgical route; and generating the alloy by melting thefirst blended body and a third metal and a fourth metal by means of amelt metallurgical route; wherein the first metal, the second metal, thethird metal, and the fourth metal are selected from the group consistingof the metals, niobium, zirconium, tantalum, and tungsten.
 10. Themethod according to claim 9 further comprising using the alloy as a basematerial of an implantable medical device.
 11. The method according toclaim 9, further comprising additionally grinding one of the third andfourth metals to form one of a third or a fourth metal powder andadditionally mixing one of the third and fourth metal powder with thefirst and second metal powders to form the first blended powder.
 12. Themethod according to claim 9, further comprising: grinding the thirdmetal to form the third metal powder; generating a first additional bodyfrom the third metal powder by means of the powder metallurgical route,before generating the alloy; wherein generating the alloy comprisesconcurrent melting the first blended body, the first additional body,and the remaining metal by means of the melt metallurgical route.